On using the tool the picture 'jumps' & top of the screen a message "Not responding" appears. Using the mouse ot graphic tablet, the result is the same.
Why is this?
HP Pavilion dv7 64bit windows7
Yep, that's the infamous "10 second bug", a known problem with the software.
The workaround is to first hold down your left mouse button on the area at the bottom that shows the image info:
Keep the mouse button held down for about 10 seconds -- until the Editor gets the "Not Responding" message. Then release the mouse button and the Lasso Tool will work OK.